The present invention relates to the recovery of oil from waste and, more particularly, to the recovery of oil from oily waste from oil refineries.
Oily waste having a heavy hydrocarbon portion and inert solids is carried in aqueous streams derived from diverse sources in an oil refinery, such as treatment lagoons, oily water systems, tank cleanings, and the like. Recovery of oil from this material is especially difficult due to the water content of the streams.
Processes are known which clean up and dispose of aqueous industrial wastes, sewage, brackish or salt waters, and other aqueous material, in part by evaporating the water of the aqueous material. In one process of the above type, exemplified by the process disclosed in U.S. Pat. No. 4,007,094 in the name of Charles Greenfield et al, the aqueous waste is mixed with a fluidizing oil, the water of the mixture is evaporated in a multiple-effect evaporation system, the fluidizing oil is recovered and recirculated, and waste solids are recovered by means of a centrifuge. The waste solids obtained by centrifuging still certain some oil. If recovery of this remaining oil from the solids is required, a hydroextractor is needed which passes steam through a chamber containing the waste solids to remove the remaining oil in the solids. Such a hydroextractor is disclosed as a cake deoiler in U.S. Pat. No. 4,289,578 to Charles Greenfield et al. The fluidizing oil multiple-effect evaporation process just described is effective but produces dry waste solids, which must still be disposed of. In addition, the process requires a substantial investment in equipment, which renders the process costly.
Many oil refineries have existing equipment for the production of coke by a delayed coking process. In a copending application assigned to the assignee of the present application, Ser. No. 185,617, filed on Apr. 25, 1988, now U.S. Pat. No. 4,868,407 it has been proposed to dispose of refinery sludges having high water content and solids by feeding them into a delayed coking system. In the process disclosed in that application, the wet sludge is fed to a blowdown drum of the delayed coking system for the removal of water.